Light-sensitive two-component diazotype materials adapted for heat development



United States Patent 3,326,686 LIGHT-SENSITIVE TWO-COMPONENT DI- AZOTYPE MATERIALS ADAPTED FOR HEAT DEVELOPMENT David I. Randall, New Vernon, N.J., and Harlan B. Freyerrnuth, Easton, Pa., assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed May 31, 1963, Ser. No. 284,364 10 Claims. (Cl. %91) This invention relates to the production of light-sensitive diazotype photoprinting materials, susceptible, after exposure to actinic light under an opaque pattern having a relatively translucent background, to development of an azo dye image corresponding to the pattern by heating.

According to US. Patent 2,653,091 to Greig, it was known to produce light-sensitive diazotype photoprinting materials susceptible to heat development by coating a base such as paper with a sensitizing composition containing a stabilized light-senitive diazonium compound and an azo coupling component together with trichloroacetic acid as a stabilizer against coupling, and an alkali metal, ammonium or amine salt of trichloroacetic acid, the composition having a pH not less than 3. After exposure to actinic light under an opaque pattern, the resulting material yielded an image of the pattern on heating at a temperature between 100 C. and the scorching temperature of the paper. The trichloroacetic acid is apparently decomposed and the pH thus raised to a level at which coupling of the residual diazonium compound and azo coupling component occurs in the areas corresponding to the pattern.

Light-sensitive diazotype materials susceptible to heat development as disclosed in the Greig Patent are subject to the disadvantage that the relatively high acidity of the sensitizing composition causes deterioration of the paper coated therewith, impairing the storage qualities or shelf life of the product.

We have discovered that this disadvantage can be overcome by employing, in a two-component diazotype sensitizing composition and the light-sensitive layers produced therewith an alkali metal or ammonium salt of trichloroacetic acid in the absence of free trichloroacetic acid; and as a stabilizer against premature coupling, an acid stabilizer having a dissociation constant at 25 C. of at least 10 but not greater than Since trichloroacetic acid has a dissociation constant of about 2X10- at 18 C. and about 1.2 at 25 0., acid stabilizers having a dissociation constant within the aforesaid range do not liberate trichl-oroacetic acid from its salts, and the disadvantages of excessive acidity are thereby avoided.

The acid stabilizers employed in accordance with the invention are those conventionally used in two-component diazotype materialsfor example citric acid, tartaric acid, acetic acid and the like. These are used together with conventional light-sensitive diazonium compounds, as for example those referred to in US. Patent 2,501,874 and in the article by Van der Grinten in Photographic Journal, volume 92B (1952) page 46. Preferred diazonium compounds are those derived from N-monoor N,N-disubstituted-p-phenylenediamine, as for example:

p-amino-diphenylamine N-betahydroxyethyl-N-methyl-p-phenylenediamine N-betahydroxyethyl-N-ethyl-p-phenylenediamine p-ethylamino-m-toluidine p-diethylamino-aniline p-dimethylamino-aniline N-benzyl-N-ethyl-p-phenylenediamine p-dimethylamino-o-toluidine p-diethylamino-o-phenetidine "ice 4-benzoylamino-Z,S-diethoxyaniline 4-morpholino-aniline 4-morpholino-2,S-diethoxyaniline 2-amino-S-dimethylamino-benzoic acid N,N-di betahydroxyethyl) -p-phenylenediamine p- N-ethyl-N-betahydroxyethylamino -o-toluidine p-dibetahydroxyethylamino-o-chloroaniline p-ethylamino-aniline 2,5-diethoXy-4- (4'-ethoxyphenylamino -aniline p-amino-N-methylaniline p-amino-N-dimethylaniline p-arnino-N-betahydroxyethylaniline 4-amino-2-methoxy-l-cyclohexylaniline The diazonium compounds are used in the form of their salts stabilized with zinc chloride, tin chloride, cadmium chloride and the like.

Azocoupling components suitable for use in the sensitizing compositions of the invention are those commonly employed in two-component diazotype photoprinting materials, such as:

resorcinol octylresorcinol 2,5-xylenol phloroglucinol betanaphthol 2,3-dihydroxynaphthalene 2,7-dihydroxynaphthalene 2,3-dihydroxynaphthalene-6-sodium sulfonate 2-amino-8-naphthol-3,6-disodium-sulfonate 2-naphthol-3,6-disodium sulfonate alpha-resorcylic acid amide 2,3-hydroxynaphthoic-acid-hydroxyethylamide 2,2',4,4-tetrahydroxybiphenyl phloroglucinol-carboxylic acid 1,7-amino-naphthol-Z-hydroxy-8-biguanide m-hydroxyphenyl-urea acetoacetanilide 7-hydroxy-1,2-naphthimidazole 1-phenyl-3-methyl-5-pyrazolone Further additives which can be advantageously included are background stabilizers such as thiourea or thiosinamine; acceleators such as 1-allyl-3-betahydroxyethyl-2- thiourea, l-allyl-Z-thiourea and the like; humectants such as glycol or glycerine; wetting agents such as saponin, lauryl-sulphate, kerylbenzenesulfonate, or oleyl-N-methyltaurine; and image intensifiers, such as ammonium sulfate, nickel sulfate or zinc chloride. Moreover, there can 1 be include-d in the composition, finely divided silica or alumina, and/or emulsified resins such as aqueous dispersions or latices of polyvinylacetate.

In general, the quantity of the trichloroacetic acid salt employed in'the sensitizing composition should be such as to exceed the stoichiometric equivalent of the quantity of base required to neutralize the acid stabilizer present in the mixture. In general a quantity of said salt from one to three times the stoichiometrical equivalent of the acid stabilizer is suitable. Preferably, the quantity of said salt exceeds the sum of the stoichiometric equivalent of the diazonium compound and of the acid stabilizers. The proportions of the other components of the mixture are those conventionally used in diazotype sensitizing compositions.

The sensitizing composition is advantageously applied in the form of an aqueous solution as a coating to a base, especially paper or cellulosic materials such as regenerated cellulose and allowed to dry. Alternatively, a base such as paper sensitized with a conventional twocomponent diazotype sensitizing composition can be treated e.g., by spraying or padding with an aqueous solution of the trichloroacetic acid salt, and then dried. In this way, the trichl-oroacetate may be concentrated in the surface stratum of the sensitized layer so that the excess is sufficient to effect development of the image in that portion of the layer, even though underlying strata of the sensitized layer may lack sufficient trichloroacetate to effect development.

After exposure under an opaque pattern to actinic light the material can then be developed at temperatures ranging from about 100 C. to the scorching temperature of the paper. Temperatures from 120 C. to 200 C. are satisfactory. In the development of the image by heating, the trichloroacetic acid salt decomposes, rendering the salt-forming alkali metal or ammonium moiety thereof available to neutralize the acid stabilizer, and thereby causing coupling of the diazonium salt with the azo coupling component.

The invention is illustrated by the following examples wherein parts and percentages are by weight unless otherwise indicated:

Example I A sensitizing solution is prepared by combining the following ingredients: Water cc 60 Glycerin cc 5 Isopropyl alcohol cc 1 Citric acid g 5 Zinc chloride g 5 N-beta-hydroxyethyl-N'-allyl-thiourea g- 2.5 2,3-dihydroxynaphthalene-6-s-odium sulfonate g 4 4-N,N-diethylaminobenzene diazonium chloride-zinc chloride double salt g 2 Saponin g 0.1 Sodium trichloroacetate g 12 Finely divided silica (1-5 microns) g 6 Water to make cc 100 This solution is coated on high grade sulfite bond paper, and dried. After exposure of the sensitized material to actinic light under an opaque pattern on a translucent supporting sheet, the sensitized material is heated to a temperature of about 120 C. An azo dye image is rapidly formed, reproducing the pattern of the original.

Example II Sulfite bond paper is coated with a sensitizing solution having the following composition:

Water cc 60 Ethyleneglycol cc 5 Isopropyl alcohol cc 1 Citric acid g 5 Zinc chloride g 5 N-beta-hydroxyethyl-N'-ally1 thiourea g 2.5 Diresorcylsulfoxide g 1.3 Acetoacetanilide g 0.07 2,3-dihydroxynaphthalene-6-s0dium sulfonate g 1.9 4-N,N-diethylaminobenzene diazonium chloride-zinc chloride double salt g 3 Sodium trichloroacetate g 14 Saponin g 0.01 Finely divided alumina l-5 microns g 6 50% aqueous corn starch dispersion cc 3 Water to cc 100 After drying, the paper yields a copy on exposure to light under an opaque pattern and heat development according to the process described in Example I.

4 Example III A paper base coated with a sensitizing solution having the following composition:

4-N,N-dimethylaminobenzene diazonium chlo- After drying the paper is exposed under an opaque pattern to ultra violet light, and then heated to l10-125 C. A copy of the pattern is readily formed.

Example IV Paper, preooated with an aqueous suspension of colloidal silica and then dried, as sensitized by coating with a sensitizing composition having the following ingredients:

Water cc Ethylene glycol cc 9 Citric acid g 5 Boric acid g 2.5 Zinc chloride g 9 Thiourea g 6 Resorcinol g 1.8

p-DiazoN-methyl-N-hydroxy-ethylaniline zinc chloride double salt g 5.5 Potassium trichloroacetate g 15 Saponin g 0.3

The resulting material is dried and exposed under a pattern to actinic light. On heating to 130 C. an image is rapidly formed, reproducing the pattern.

Instead of incorporating the trichloroacetic acid salts in the sensitizing compositions, as illustrated in the foregoing examples, the other ingredients of said compositions can be combined and applied to a supporting sheet and dried, yielding a two-component diazotype sensitized sheet of the kind heretofore used for ammonia development. An aqueous solution of alkali metal or ammonium trichloroacetate having, for example, a concentration of 1020%, can then be applied to the sensitized surface of the sheet by atomizing, padding or the like, and the sheet again dried. In this way the surface portion of the lightsensitive layer includes the trichloroacetate salt in a quantity exceeding the stoichiometric equivalent of base required to neutralize the acid stabilizer in the same portion of the layer, even though the total quantity of acid stabilizer contained in the surface layer and underlying layer may exceed the stoichiometric equivalent to the trichloroacetate. The material thus sensitized can be developed after exposure to actinic light under an opaque pattern, by heating to a temperature above 100 C., causing decomposition of the trichloroacetate with generation of sufiicient alkaline reacting residue to cause imagewise coupling of the two-component diazotype composition in the surface portions of the light-sensitive layer.

Instead of sodium, potassium and ammonium salts of trichloroacetic acid employed in the foregoing examples, neutral salts of other bases which are themselves otherwise unreactive or inert toward the ingredients of the sensitizing composition can be used, e.g., the other alkali metal salts, alkaline earth metal salts and nitrogen base salts, trichloroacetates of mono-, diand tri-ethanolamine, or of triethylenetetramine, benzylamine or trimethylamine.

Other variations which will be obvious to those skilled in the art can be made in the compositions and processes set out above without departing from the scope or spirit of the invention.

We claim:

1. A sensitizing composition for diazotype photoprinting material comprising, in aqueous medium, an azo coupling component, a light-sensitive diazonium salt, an acid stabilizer against coupling, all such stabilizers of the composition having a dissociation constant at 25 C. Within the range of to 10- and a neutral saltof trichloroacetic acid selected from the class consisting of sodium, potassium and ammonium salts, in an amount exceeding the stoichiometric equivalent of the amount of base required to neutralize said acid stabilizer.

2. A sensitizing composition as defined in claim 1 wherein the amount of said trichloroacetic acid salt is in excess of the stoichiometric equivalent of said diazonium salt plus the stoichiometric equivalent of the amount of base required to neutralize said acid stabilizer.

3. A sensitizing composition as defined in claim 1 wherein the said light-sensitive diazonium salt is a zinc chloride double salt derived from a diazotized N-substituted pphenylenediamine.

4. A sensitizing composition as defined in claim 1 wherein the said acid stabilizer is citric acid.

5. A sensitizing composition as defined in claim 1 wherein said trichloroacetic acid salt is sodium trichloroacetate.

6. Light-sensitive diazotype photoprinting material comprising a supporting sheet having thereon a light-sensitive surface layer comprising an azo coupling component, a light-sensitive diazonium salt, an acid stabilizer against coupling, all such stabilizers of said layer having a dissociation constant at 25 C. within the range of 10 to the 10 and a neutral trichloroacetic acid salt of the class consisting of sodium, potassium and ammonium salts, the amount of said salt in at least the surface portion of said layer exceeding the 'stoichiometric equivalent of the (3 amount of base required to neutralize the acid stabilizer in said surface portion of said layer.

7. Light-sensitive diazotype photoprinting material as defined in claim 6, wherein the amount of said salt in the surface portion of said layer exceeds the stoichiometric equivalent of said diazonium salt plus the stoichiometric equivalent of the amount of base required to neutralize said acid stabilizer in said surface portion of said layer.

8. Light-sensitive diazotype photoprinting material as defined in claim 6, wherein said light-sensitive diazonium salt is a zinc chloride double salt derived from a diazotized N-substituted p-phenylenediamine.

9. Light-sensitive diazotype photoprinting material as defined in claim 6, wherein said acid stabilizer is citric acid.

10. Light-sensitive diazotype photoprinting material as defined in claim 6, wherein said trichloroacetic acid salt is sodium trichloroacetate.

References Cited UNITED STATES PATENTS 2,653,091 9/ 1953 Greig 96-49 3,046,128 7/1962 Klimlcowski et al. 26-91 X 3,220,846 11/1965 Tinker et al. 9691 FOREIGN PATENTS 1,249,9l3 ll/l960 France.

861,601 7/1959 Great Britain.

NORMAN G. TQRCHIN, Primary Examiner. J. TRAVIS BROWN, Examiner.

C. L. BOWERS, Assistant Examiner. 

1. A SENSITIZING COMPOSITION FOR DIAZOTYPE PHOTOPRINTING MATERIAL COMPRISING IN AQUEOUS MEDIUM AN AZO COUPLING COMPONENT, A LIGHT-SENSITIVE DIAZONIUM SALT, AN ACID STABLIZER AGAINST COUPLING, ALL SUCH STABILIZERS OF THE CONPOSITION HAVING A DISSOCIATION CONSTANT AT 25*C. WITHIN THE RANGE OF 10**-1.5 TO 10**-5, AND A NEUTRAL SALT OF TRICHLOROACETIC ACID SELECTED FROM THE CLASS CONSISTING OF SODIUM, POTASSIUM AND AMMONIUM SALTS, IN AN AMOUNT EXCEEDING THE STOICHIOMETRIC EQUIVALENT OF THE AMOUNT OF BASE REQUIRED TO NEUTRALIZE SAID ACID STABILIZER. 